Food-deprived activity stress decreased the activity of the histaminergic neuron system in rats

The hypothalamus, which is rich in histaminergic neurons, is highly sensiti ve to aversive stimuli such as stress. Histamine H-3 receptors, which regul ate histamine release from the presynaptic site, are associated with stress -induced brain activity. In this study, we investigated the changes of hist amine content and histamine H-1 and H-3 receptors in the brains of rats sub jected to stress-induced through food deprivation and physical activity on a running wheel (food-deprived activity stress). For purposes of comparison , we also examined the stressful effects of forced swimming on the histamin ergic neuron system of rats. The H-3 receptor density rapidly declined in t he acute phase of stress but gradually returned to the control level in the chronic phase. On the other hand, the H-1 receptor slowly decreased and re mained at a low level during the chronic phase. These results reveal that t here is a discrepancy between the levels of H-1 and H-3 receptors in the ac ute and chronic phases of stress. Brain histamine content gradually increas ed during the late phase of both food-deprived activity stress and forced s wimming stress. These changes presumably resulted in the inhibition of hist aminergic neuronal activity in the chronic stress condition. In accordance with this hypothesis, the intraventricular administration of histamine sign ificantly reduced the hyperactivity caused by food-deprived activity stress . Since extensive exercise and restricted feeding are thought to be associa ted with anorexia nervosa, the abnormalities in the histaminergic neuron sy stem might contribute to trait status in anorexia nervosa. (C) 2001 Elsevie r Science B.V. All rights reserved.